1. Field of the Invention
This invention is generally concerned with the production of attrition-resistant binder formulations such as those used to bind catalyst particles into those forms (e.g., microspheroids) which are commonly employed in fluid catalytic cracking processes. More particularly, this invention is concerned with the use of certain inexpensive, naturally occurring clay materials, e.g., kaolinites--in place of certain more expensive, synthetic materials, e.g., synthetic silica and/or alumina materials--as principle ingredients in such binder formulations.
2. Description of the Prior Art
Clays have been used in catalyst matrix systems for many years. For example, one very important development in petroleum "cracking" was the catalytic decomposition of gas oil in the presence of certain naturally occurring clays such as kaolinites in an atmosphere of the gas oil's own vapor. However, the use of such clays as catalysts per se has diminished over the years. There were several reasons for this. One of the most important of these reasons was the fact that most naturally occurring clays lack the quality of "attrition-resistance" which is very important in any catalytic system which places its catalyst particles in "fluid motion." Moreover, catalytic clays of this type also have to be extensively treated before they can be used as "cracking catalysts." For example U.S. Pat. No. 2,848,423 notes that in order for its particular process to be effective, its kaolin catalyst ingredient first has to be "sized" in order to obtain kaolin particles of less than about 2 microns. These sized particles are then aggregated and subjected to elevated temperatures. The resulting materials are thereafter treated with hydrogen sulfide at about 1200.degree. F. in order to form aggregates which, in turn, are exposed to ammonium chloride in order to selectively remove any iron present in the kaolin aggregates.
The need for so many preparatory steps, in conjunction with the fact that catalyst particles having high kaolin concentrations are subject to unacceptable attrition losses, provided a great deal of motivation to find more suitable catalyst materials. Eventually a large variety of other amorphous catalytic materials, and especially those having large proportions of alumina, were developed. The use of these materials represented a very significant step in this art because not only were these other alumina-containing materials more catalytically active than kaolin clays, they also were generally much more attrition-resistant. Later it was found that certain naturally occurring, crystalline zeolite materials such as y-faujasites also made very effective catalysts. They too proved to be generally more attrition-resistant than naturally occurring clays. However, because of their small crystalline sizes, naturally occurring zeolite particles have to be bound together with an attrition-resistant binder system in order to render them suitable for use in fluid catalytic cracking units (FCC units). Still later, whole classes of very effective synthetic, crystalline, zeolite catalysts, e.g., ZSM-5 were developed. Here again, since these synthetic zeolites also have very small crystalline sizes (e.g., average diameters of less than about 5 microns), they too have to be bound together in larger particle units by various "binder" or "glue" formulations. Those made of silica, alumina, silica/alumina, silica/magnesia, etc. are commonly employed for such purposes.
It also should be noted that not only do many of these glue or binder materials serve as attrition-resistant binder matrices, they also often serve as catalysts in their own right. This independent catalytic activity has proved to be an advantage in catalyzing some chemical reactions, but a disadvantage in catalyzing many others. Moreover, many of these glue or binder materials also are chemically reactive with many of the different kinds of catalyst particles they are called upon to bind together. Such chemical reactivity between a given binder material and a given species of catalyst particle may be an advantage in some cases, but generally speaking it is not considered to be an advantage; and in many cases it may well constitute a serious detriment to the catalytic activity of a given species of catalyst.
Those familiar with this art also will appreciate that most binder formulations can be used in at least five different ways, e.g., (1) they can be used to "glue together" (hence their appellation "binder" materials) various catalyst particles into larger catalyst matrices, especially in those cases where the catalyst particles are so small that they would be susceptible to unacceptable elutriation losses, (2) they can be used to grow, in situ, certain lattice structures useful in forming catalyst matrices, (3) they can be impregnated with liquid catalyst solutions such as those of various Group VIII metals, (4) they can be introduced as catalytically inert binder particles into various chemical processes in order to "dilute" the concentration of, and hence the activity levels of, active catalyst particles being used in said processes and (5) they can be used as catalytically active materials in their own right; that is to say they can simultaneously serve both as a "binder" and as a "catalyst".
The need to perform so many varied catalytic functions also has resulted in an ever expanding need for catalyst materials of greater and greater complexities. Because of this, catalyst particles having more than one species of active catalyst are often employed to simultaneously carry out several different catalytic duties. For example, use of several different kinds of zeolite catalysts, e.g., the use of zeolite catalysts and amorphous catalysts, in the very same particle has proven to be an effective technique in such varied chemical processes as hydrocracking, alkylation, dealkylation, transalkylation, isomerization and polymerization. Many low-soda exchanged Y-zeolite catalysts and ultra-stable Y-zeolite catalysts also are known to be especially useful when agglomerated into multi-catalyst-containing particles.
The use of such multi-component catalysts also has led to a need for more and more "universally non-reactive" binder materials. That is to say that the need for more complex catalyst particles has intensified the need for binder materials which are capable of binding several kinds of catalyst particles into suitable forms (e.g., into microspheroidal particles) without the binder either entering into undesired chemical reactions with any of the different catalyst species in a given particle or without the binder entering into the catalytic reaction(s) being catalyzed by that particle. At present, various complexes of alumina, alumino-silicate compounds, silica, magnesia, silica-magnesia, chromia, zirconia, gallium, germanium, etc., are the materials most widely employed as "universal" binders. For the purposes of this patent disclosure, all such universal binder materials may be thought of as being--and referred to as--"glue" or "binder" materials. That is to say that--if they are not to be used in their own right as catalytic materials--their chief function is to "glue" various active catalyst particles together to form larger particles. However, as was previously noted, many of these universal binder materials are in fact catalytically active in certain catalytic environments where it would be more advantageous if they were completely inert.
Those skilled in this art also will appreciate that regardless of the specific catalytic duties to which a given binder material is put in a given fluid catalytic process, elutriation losses will occur when particles of different sizes, shapes and/or velocities undergo inter-particle impacts. Such impacts tend to shatter or otherwise damage the matrices of all such materials. Hence, smaller and smaller fragments are constantly being formed and subsequently lost via cyclone elutriation of the resulting smaller particles. Fragments having diameters of less than about 20 microns are especially susceptible to elutriation losses.
Other losses occur as a result of differences in the densities of two or more catalyst species used in the same "fluid" process. That is to say that in many modern catalytic cracking processes, it is not at all uncommon to have as many as a half dozen different kinds of catalyst species simultaneously circulating through a reaction system in order to carry out distinctly different catalytic functions. Consequently, classification and sequestration are often caused by the action of a mass of reaction vapors sweeping through and separating different kinds of catalyst particles according to their density differences. Consequently, use of the very same binder material to make different catalyst species is a widely employed practice since it tends to create like densities in the different particle species. Thus, for all of the above noted reasons, the catalyst-employing chemical arts have an ongoing interest in developing more attrition-resistant, "universal", binder formulations.
The catalytic arts also have long recognized that certain naturally occurring clays have those "universal" binding qualities which are so useful in formulating a wide variety of catalysts. However, prior art attempts to use such clays in catalyst formulations have been thwarted time and again by the fact that those binder materials having large proportions of such clays are usually much too "soft" for use in fluid catalytic systems. That is to say that most high clay content binder or catalyst materials generally lack the quality of "toughness" or "attrition-resistance"; and, hence, easily succumb to those forces associated with particle impacts which eventually lead to the creation of smaller particles and unacceptable elutriation losses. Consequently, the role of naturally occurring clays in the catalytic arts has steadily decreased since the 1930's when they were widely used as petroleum cracking catalysts. At present, naturally occurring clays such as kaolin are used sparingly as catalysts or as binder materials, and then only in conjunction with much larger proportions of those alumina, silica-alumina, silica-magnesia, zeolite, etc., "glue" type materials previously noted.
Naturally occurring clays do, however, continue to play somewhat larger roles in some catalyst formulations as "filler" ingredients. In this "filler" capacity, such clays (in conjunction with various inorganic glues of the types previously described) are used in order to give "body" to certain catalyst matrices at the lowest possible costs. Perhaps the most important property of a clay for fulfilling such a "filler" function is that it be chemically inert with respect to the catalytic ingredients employed in a given formulation. As was previously noted, this same characteristic also is useful when a clay is used as a "binder" material. However, the role of a clay "filler" is not exactly the same as that of a clay "binder" in the herein described processes. For example, a clay "filler", most preferably, will not enter into chemical reactions with any of the other ingredients in the binder formulation. On the other hand, when acting as a "binder", a clay ingredient, most preferably, will react to some limited degree with some other ingredient in the binder formulation. As will be seen in later parts of this patent disclosure, applicant's clay ingredient chemically reacts with a phosphate-containing ingredient to form a viscous reaction product. This reaction product, once formed, should not, however, chemically react with any catalyst particles which are subsequently introduced into the formulation.
It also should be emphasized that in these filler applications, certain clays may comprise high percentages (e.g., higher than about 10 percent by weight) of the overall catalyst formulation; but, again, in such cases, they act as completely inert "fillers" and not as either "active catalysts" or as "binder materials". Those skilled in this art also will appreciate that filler clays also should have certain particle sizes and/or morphologies. Typically, certain inert kaolin clay materials having particle sizes less than about 0.25 microns are employed for use in such "filler" capacities. Moreover, the use of so-called "ball" clays (as opposed to "plate" or "rod" forms) is a highly desired--and sometimes mandatory--attribute of those filler clay particles used in proportions larger than about 10 percent. Absence of these qualities normally will detract from the attrition-resistance of any particles in which clays serve as fillers. On the other hand, clays used in binder roles generally do not have as stringent size and morphology restrictions.
The fact remains, however, that since naturally occurring clays are so much less costly than the alumina, silica, etc. "glue" materials previously noted, and since they can bind so many different kinds of catalyst particles without chemically reacting with them, and since they are catalytically inert with respect to so many chemical reactions, binder formulations having large clay proportions would be very welcome additions to the catalyst-employing arts--if the attrition problems currently associated with their use as binders (as opposed to their use as fillers) could somehow be obviated.
It also should be noted that binder and/or catalyst matrix attrition problems arising from the presence of large proportions of such clays have been addressed through the use of greater proportions of "hard" binder and/or catalyst ingredients (and especially through the use of greater proportions of hardness-imparting "glue" or catalyst ingredients). That is to say that, in the past, attrition-resistance problems with clay-containing catalyst particles have been addressed by using relatively less clay and relatively more hardness imparting ingredients such as alumina and/or silica. Attrition-resistance problems also have been addressed--incidentally--through the use of various chemical treatments which are primarily employed to implement, improve or diminish the catalytic activities of various active catalyst materials. By way of example only, U.S. Pat. No. 4,594,332 recognizes such activity/hardness interrelationships in that it teaches production of hard, fracture-resistant binder systems from zeolites of the pentasil family by use of a process wherein water, organic additives such as hydroxyethylcellulose and a silicate are added to zeolite particles so that the resulting particles are rendered both more catalytically active and more attrition-resistant. However, this favorable outcome is not the usual case; indeed, very often catalytic activity must be "sacrificed" in direct proportion to any gains made in attrition resistance.
Another set of problems associated with production of attrition-resistant catalyst particles follows from certain inherent restrictions which must be placed upon those so-called "gel reaction" processes which are commonly employed to make many kinds of catalysts. For one thing, they must be carried out in some rather restricted pH ranges (especially those confined to alkaline, i.e., 8.0 to 14.0 regions of the pH scale). For example, the gel reaction step of U.S. Pat. No. 4,471,070 (the 070 patent) is restricted to a 8.5 to 10.5 pH range. Similarly, the gel reaction taught by U.S. Pat. No. 4,728,635 (the 635 patent) is preferably carried out in a 7.0 to 10.5 pH range.
The rather narrow, alkaline, pH limitation placed upon the process taught by the 070 patent follows from the fact that higher pH values would force a chemical shift which favors the formation of alkaline aluminum, i.e., the aluminate anion, AlO.sub.2.sup..THETA.. However, aluminate anions are soluble in water and therefore subject to being "washed out" during subsequent filtration steps to which these materials must be submitted. Similarly, the 635 patent teaches use of aluminum oxide in an alkaline medium of magnesium compounds in order to attain a distinctly alkaline ionization medium. Under such conditions, small dispersed particles of aluminum oxide having maximum effective surface areas are rapidly associated with water molecules and thereby establish an equilibrium which also favors the anionic form of aluminum as its aluminate (i.e., AlO.sup..THETA..sub.2) ion. Many other gel reactions have similar restrictions to the use of mildly alkaline reaction systems. Indeed, the prior art has, to a large degree, accepted the idea that any attempts to carry out gel reactions in either a strongly basic or a strongly acidic reaction system will usually lead to some degree of damage to aluminum-containing molecules which tends to weaken any catalyst matrix made from them.
This restriction of the prior art to mildly alkaline reaction conditions has several implications which bear upon the novelty and scope of applicant's invention because the chemical reactions of the herein described processes can be--and in many instances preferably are--carried out in strongly acidic conditions as well as in strongly alkaline ones. This fact indicates that applicant's reactions are qualitatively different from the "gel reactions" employed by the prior art. Thus, applicant's processes can be distinguished from much of the prior art by the fact that they have both "acid versions" and "alkaline versions". Regardless of the version employed, however, the most important aspect of applicant's processes remains the fact that they can employ large proportions of naturally occurring clays in order to produce binder matrices (and binder/catalyst matrices) without thereby rendering those matrices too "soft" for use in fluid catalytic processes. The fact that extremely high levels of attrition-resistance can be achieved without "sacrificing" the catalytic activity of any active catalyst particles which may be placed in applicant's binder systems also is a most important aspect of these processes.